A continuation and an extension of our studies on the enzymatic synthesis of fatty acids and cholesterol is proposed. These studies are directed towards a further understanding of the structural organization of the fatty acid synthetase complexes of avian and mammalian liver, the mechanism of fatty acid synthesis, the identification of factors that regulate the levels and activities of fatty acid synthesizing enzymes, the mechanisms of these regulations, and the identity of the genetic factors regulating fatty acid synthesis. Studies on cholesterol synthesis are primarily concerned with the isolation, structural organization and mechanism of action of enzymes converting mevalonic phosphate to squalene. Specific objectives of these studies are the following: (1) Fatty acid synthesis ((a) the determination of the structural organization of each of the nonidentical half-molecular weight sub-units of fatty acid synthetase complexes, (b) the determination of the kinetics of triacetic lactone formation, NADPH binding, and the partial reactions of fatty acid synthesis effected by subunits and enzyme complex, (c) the purification to homogeneity of the enzymes effecting the interconversion of apo-, holo-a- and holo-b-fatty acid synthetases, (d) the identification of factors controlling fatty acid synthetase activity and the determination of their mechanism of action, (e) the isolation of mRNA for the fatty acid synthetase, the synthesis of fatty acid synthetase in a cell-free system in the presence of this mRNA, and the quantitation of this mRNA in liver as a function of hormonal or nutritional state of the animal); and (2) Synthesis of cholesterol ((a) the purification and mechanism of action of enzymes effecting the conversion of mevalonic phosphate to sqalene, and (b) the determination of the structural organization of squalene synthetase and its mechanism of action).)